This invention relates to servomechanisms for position control of the read and write transducers on the rotating disk of a magnetic recording disk file, and in particular to a magnetic recording disk having a specific pattern of pre-recorded servo signals for providing sampled position signals to the control system.
In certain magnetic recording disk files which have a relatively high density of data tracks, it is necessary to provide servo control of the read and write heads to both maintain the heads over the tracks in the presence of various disturbances and to quickly and accurately position the heads to other tracks for subsequent read and write operations. In order to accomplish this, certain conventional disk files utilize pre-recorded servo signals on either a dedicated servo disk or the data disk to provide a position error signal (PES) to the control system. One well known method of incorporating this servo information is to record the information on a separate dedicated disk and use a servo read head on that disk to imply the location of read/write heads on the same actuator on other data disks within a given tolerance limit. In this scheme, the control system can receive a continuous PES to permit very accurate positioning of the servo head, but the read/write heads suffer track misalignment to a given tolerance limit due to thermal effects and mechanical effects such as disk flutter. Another well known method of incorporating this servo information is to place pre-recorded servo signals on equally angularly spaced sectors which extend out radially from the data disk center. Thus, as the disk rotates, the read/write head or a dedicated servo read head receives sampled position signals as the sectors pass beneath the head. Because in this method the sectors of servo information are recorded on the disk between sectors of data, there is less surface area available on the disk for data. Typically the sector servo pattern occupies from 10% to 20% of the available disk recording surface area. While it is thus desirable to minimize the amount of disk surface area required for the servo information, it is also necessary to maximize the number of servo sectors in order to obtain as high a sampling rate as possible to generate the PES for the control system.